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The Digestive System
and Body Metabolism
Premedical Biology
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Digestive System and Body
Metabolism
 Digestion
 Breakdown of ingested food
 Absorption
 Passage of nutrients into the blood
 Metabolism
 Production of cellular energy (ATP)
Organs of the Digestive System
Organs of the Alimentary Canal
 Mouth
 Pharynx
 Esophagus
 Stomach
 Small intestine
 Large intestine
 Anus
Mouth (Oral Cavity) Anatomy
 Lips (labia)
 Cheeks
 Hard palate
 Soft palate
 Uvula
Mouth (Oral Cavity) Anatomy
 Vestibule
 Oral cavity
 Tongue
Mouth (Oral Cavity) Anatomy
 Tonsils
 Palatine tonsils
 Lingual tonsil
Processes of the Mouth
 Mastication (chewing) of food
 Mixing food with saliva – ptyalin (amylase)
 Initiation of swallowing by the tongue
 Allowing for the sense of taste
Sweet, sour, bitter, tangy, spicy,
taste buds
nerve cells
10,000 taste cells
papillae
cover the tongue, palate,
epiglottis, and pharynx
Each taste cell consists of small
hairs that lie in the taste pore.
There, dissolved food or drink
binds to a receptor, like a key in
a lock.
Pharynx Anatomy
 Nasopharynx –
not part of the
digestive system
 Oropharynx
 Laryngopharynx
Layers of Alimentary Canal Organs
 Mucosa
 Surface epithelium
 Small amount of connective tissue
(lamina propria)
 Small smooth muscle layer
Layers of Alimentary Canal Organs
 Submucosa
 Soft connective tissue with blood
vessels, nerve endings, and lymphatic
tissue
Layers of Alimentary Canal Organs
 Muscularis externa – smooth muscle
 Inner circular layer
 Outer longitudinal layer
 Serosa
 Outermost layer – visceral peritoneum
 Layer of serous fluid-producing cells
Stomach Anatomy
 the cardioesophageal sphincter
 Regions
 Cardiac region – near the heart
 Fundus
 Body
 Phylorus –terminal end
 the pyloric sphincter
Stomach Anatomy
Stomach functions and Mucosa
 storage tank, chemical breakdown
 chyme (processed food)
 Gastric pits formed by folded mucosa
 Simple columnar epithelium:
Mucous neck cells – produce a sticky alkaline
mucus
Gastric glands:
Stomach glands
• Chief cells – produce protein-digesting
enzymes (pepsinogens)
• Parietal cells – produce hydrochloric acid
• Endocrine cells – produce enteroglukagon,
gastrin, somatostatin
Glands and specialized cells are in the
gastric gland region
Structure of the Stomach Mucosa
Small Intestine
 The body’s major digestive organ
 Site of nutrient absorption into the blood
 Duodenum
 Jejunum
 Ileum
Chemical digestion
 Source of enzymes that are mixed with
chyme
Intestinal cells
Pancreas
 Bile enters from the gall bladder
Chemical digestion
Microvilli of the Small Intestine
 Folds and Villi of Mucose
 Called circular folds - folds of the mucosa
and submucosa
 Villi with blood and
lymphatic capillaries
The submucosa has
Peyer’s patches
(lymphatic tissue)
Microvilli of the Small Intestine
 Microvilli found on absorptive cells
Digestion in the Small Intestine
 Enzymes
 Break double sugars into simple sugars
pancreatic amylase
 Complete some protein digestion
exopeptidase and endopeptidase: trypsin,
chymotrypsin
 Pancreatic enzymes play the major
digestive function (lipase)
Absorption in the Small Intestine
 Water is absorbed along the length of
the small intestine
 End products of digestion
 Most substances are absorbed by active
transport through cell membranes
 Lipids are absorbed by diffusion
 Substances are transported to the liver
by the hepatic portal vein or lymph
Structures of the Large Intestine
 Colon
 Ascending
 Transverse
 Descending
 S-shaped sigmoidal
 Rectum
 Anus – external body opening
Large Intestine
Functions of the Large Intestine
 Absorption of water
 Eliminates indigestible food from the
body as feces
 Does not participate in digestion of food
 Goblet cells produce mucus to act as a
lubricant
 Resident bacteria digest remaining
nutrients
Accessory Digestive Organs
 Salivary glands
 Teeth
 Pancreas
 Liver
 Gall bladder
Salivary Glands and Teeth
 Saliva-producing glands
 Parotid glands – located anterior to ears
 Submandibular glands
 Sublingual glands
 Humans have two sets of teeth
 Deciduous (baby or milk) teeth
Teeth
 Permanent teeth
 Replace deciduous teeth beginning
between the ages of 6 to 12
 A full set is 32 teeth, but some people do
not have wisdom teeth
Classification of Teeth
 Incisors
 Canines
 Premolars
 Molars
Regions of a tooth
 Crown – exposed
part
 Outer enamel
 Dentin
 Pulp cavity
 Neck
 Region in contact
with the gum
 Connects crown to
root
Liver
 Largest gland in the body
 Located on the right side of the body
under the diaphragm
 Consists of four lobes suspended from
the diaphragm and abdominal wall
 Connected to the gall bladder via the
common hepatic duct
Role of the Liver in Metabolism
 Several roles in digestion
 Plays a central role in metabolism
 Detoxifies drugs and alcohol
 Degrades hormones
 Produce cholesterol, blood proteins
(albumin and clotting proteins)
Processes of the Digestive System
 Peristalsis
 Segmentation – moving
materials back and forth
to aid in mixing
Thank you for your attention
Campbell, Neil A., Reece, Jane
B., Cain Michael L., Jackson,
Robert B., Minorsky, Peter V.,
Biology, Benjamin-Cummings
Publishing Company, 1996 –
2010.